Bug 29352: Runtime parameter labels should not be said to be optional

Bug 29352: Runtime parameter labels should not be said to be optional

This patch alters the form shown when using the "Insert runtime
parameter" button in SQL reports. It makes the label field required and
removes "optional" from the field hint.

To test, apply the patch and go to Reports -> Create from SQL.

 - Click the "Insert runtime parameter" button and select "Authorized
   value."
 - Clear the "parameter label" field and click "Insert parameter."
 - The form should display an error asking you to fill in the label
   field.
 - Test that the category field is also required.
 - Close the modal and select a different runtime parameter.
 - Test again that the label field is required.
 - Test that the form submits correctly when the label field is
   populated.

Signed-off-by: Andrew Fuerste-Henry <andrew@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>